Any time you use any works that are not your own, you need to provide a citation. Citation shows the research you have done, strengthens and supports your argument, allows your audience to trace the original item for follow up, and differentiates your original ideas from the work of others.
How to cite an image in APA style:
Image creator's Last Name, First Name. (Year images was made). Title of image in italics [medium of image - i.e file type]. Retrieved from http://.....
How to cite an image in MLA style:
Image creator's Last Name, First Name. Title of image in italics. Date of creation. File Type.
How to cite an image in Chicago style:
Image creator's Last Name, First Name. Title of image in italics. Place of Publication: Publisher, Year of Publication, Type of Image, URL (date accessed) [if electronic].